A known tandem image forming apparatus includes photoconductors in association with each color of yellow, magenta, cyan and black. Such a tandem image forming apparatus can print in color at substantially the same speed as printing in monochrome, because the photoconductors are provided in association with each of the colors.
As disclosed in, for example, Japanese Laid-Open Patent Publication No. 2001-305828, a tandem color image forming apparatus is provided with image forming units, each including a developing roller and a photoconductor, arranged in the horizontal direction. In the color image forming apparatus, the width of an intermediate transfer belt is set smaller than the length of the photoconductor to reduce slidable contact between the intermediate transfer belt and the photoconductor edges. Thus, the intermediate transfer belt is prevented from being damaged or broken by a grounding layer of the photoconductor.
In the color image forming apparatus, toner carried on the developing roller may sometimes leak from the image forming units and drop onto the intermediate transfer belt. The toner dropped onto the belt is generally collected by a cleaning unit. The width of the cleaning unit is greater than the width of the intermediate transfer belt.
To reduce the size of the image forming apparatus, it would be desirable to downsize the cleaning unit such that the width of the cleaning unit becomes smaller than the width of the intermediate transfer belt.
If the toner dropped from one image forming unit onto the intermediate transfer belt is conveyed to a photoconductor of another image forming unit disposed downstream of the image forming unit in a traveling direction of the intermediate transfer belt, the toner may be adversely transferred onto the photoconductor. If the toner adversely transferred onto the photoconductor is collected by the developing roller, the color toner contained in one image forming unit, which leaks the toner therefrom, is mixed into the other image forming unit disposed downstream of the image forming unit. Thus, the toner of different colors is mixed, resulting in the contamination of the toner of the other image forming unit. If a side sealing member slides with a peripheral surface of the developing roller at its each end, the side seal member is contaminated with the different color toner.